More 4.0 oil leakage into the intake box

okay, so there is some background to this issue. the original engine in my 88 MJ was leaking horribly out of everywhere, never could figure it out. well eventually it started knocking so i replaced the engine with a working lower mileage unit. took the old one apart to find a hole in piston #6. i assume that it started as a crack or a small hole so it was pushing pressure through the piston and into the crank case causing the oil to leak out of every seal.

so after i replaced the engine i didn't have the issue any more, problem solved right? nope.

before, i was also getting oil through the CCV? hose (the largest one towards the front of the valve cover, which goes to the intake box) and it was so bad that i would leave puddles of oil everywhere from the air box. before the problem was solved (the new engine) i purchased new vacuum line loom set, including the small line towards the back of the valve cover that feeds into the intake manifold, and that slowed down the problem. the problem has now surfaced back to my new engine, and i cannot comprehend why.

I have been driving on the new engine for a few months now, including lots of highway driving. it wasn't until last week when i went wheeling when it started getting oil in the intake again.

the new engine is not completely stock, so i will list the non-stock things in it that might be contributing?

-mild comp cam
-bosch type 3 injectors
-melling high volume oil pump
-pacesetter header

thats really the only direct engine mods I've done. still running stock intake and full exhaust w/cat. I'm also running 10w-40 oil (don't have to worry about the cold here in SoCal).

one more note. since i have no idea if this could be linked, but i'll put it in here anyway. we went wheeling in a rather high elevation (10,000 ft) and i noticed that it seems to idle low (300 rpms) while in the high altitude. there were 4 other XJs w/4.0s there that did not see this affect while up there. i think it might not be adjusting to the high altitude properly?

so, if anyone has any ideas/theories/hunches as to what could be causing this problem to resurface, please reply!


edit: i should note that it only leaks with constant highway driving. around town and while wheeling it leaks much much less

Check compression. May have a bad ring or something. CHeck freeze plugs. May Also indicate a bad ring. I had it pretty bad and cleaned the assembly off the back of the valve case. Then detached the front and put a breather off the tube using foam from a fuel cell. Along with replacing the valve cover. Haven't gotten a drop on the breather since.

One big help may be to pull, clean the valve cover, and shorten the tubes that are attached to the vents on the top inside. There are some good mod threads here on doing that.

Also, you can increase the CCV orifice diameter, small rear line on the valve cover to intake manifold, a little that controls the crankcase vent rate. The IAC should compensate and keep the idle at about 750 rpm.

Throw a vacuum gage on and run a test.

Mike Mike said:

Throw a vacuum gage on and run a test.

Click to expand...

X2 on that. Cheap tool, yields a world of great info in a minute or two. Very easy to use..

i'll have to try all of this eventually. i work so i probably only have enough time to do a vacuum test and compression test, but if that doesn't reveal something unusual i will resort to cutting down the tubes

Not clear, but did you do this?

Cruiser’s Valve Cover Mod
Most early and even later Renix 4.0s could be bothered by excessive oil in the air cleaner box. A fix from my old days as Service Manager at a Jeep dealership follows. Information was provided to me from a buddy at JeepTech during those days. I don’t believe it ever came out in a Technical Service Bulletin.
　
Remove the valve cover and turn it over. Next, remove the fluted tubes that are now facing you by removing three screws on each. Chop 1 inch off each of them. Then, about a half inch up from the area where you just sawed them off, drill a half inch hole in the tubes so the holes will face the rear of the valve cover. Clean and de-burr/sand all rough edges nicely, clean with solvent, and reinstall. Don’t be concerned about the chintzy gaskets that will probably crumble into oblivion when you remove the fluted tubes. They can go back together without gaskets.